Ocean Acidification Effects on Marine Echinoderms

Ocean acidification, driven by the absorption of anthropogenic CO₂, is altering seawater chemistry by lowering pH and reducing carbonate ion availability. Echinoderms – including sea urchins, starfish and brittle stars – build their endoskeletons from calcium carbonate minerals that become more soluble under acidified conditions. Experimental and field studies demonstrate that reduced pH can slow calcification, shift skeletal mineralogy towards less stable forms and weaken test and spine integrity. These changes compromise defence against predation, impair locomotion and affect righting and sheltering behaviours. In juveniles and larvae, acidification can delay development, reduce survival and alter larval morphology, with implications for recruitment and population dynamics. Physiological stress responses, such as altered acid–base balance, energy allocation and immune function, have been recorded under combined acidification and warming. At the community scale, reduced urchin density may cascade to affect algal assemblages and habitat structure. The wide distribution and ecological importance of echinoderms mean that their responses to ocean acidification hold global significance for biodiversity, fisheries and coastal ecosystem resilience.

Research from Nature Portfolio

Recent experiments have investigated how variations in the magnesium to calcium ratio of seawater influence the mechanical properties of echinoid skeletons. When sea urchins were cultured in seawater with a lowered Mg/Ca ratio, they produced tests and spines with reduced magnesium content and diminished hardness. This reduction in nanomechanical strength suggests that future shifts in seawater chemistry, akin to ancient “calcite seas”, could render echinoderm skeletons more susceptible to physical damage and predation. Such mechanistic insights into biomineralisation under changing seawater chemistry refine our understanding of how ongoing ocean acidification may compromise echinoderm structural integrity and survival.

Research from all publishers

Analyses of Antarctic echinoderms from regions affected by hydrothermal activity reveal significant interspecific and environmental variation in skeletal magnesium content. Populations exposed to naturally lower pH and warmer temperatures exhibited reduced Mg in their high-Mg calcite skeletons, indicating local conditions modulate susceptibility to acidification. In laboratory trials on a tropical sea urchin species, combined near-future pH reduction and warming led to marginally reduced growth and altered gonad development, though calcification persisted. This work highlights the interactive effects of multiple stressors. Community-level experiments in rocky subtidal habitats demonstrate that elevated pCO₂ directly weakens coralline algae and urchin tests, while indirect diet-mediated effects further reduce test robustness. The resulting decline in urchin grazing pressure may drive shifts from barren to algal-dominated states. Together, these studies illustrate both physiological and ecological pathways through which ocean acidification reshapes echinoderm performance and marine communities.

Ocean Acidification Effects on Marine Echinoderms publication trend

The graph below shows the total number of articles in ocean acidification effects on marine echinoderms across all publications each year (not limited to Nature Index journals).

Technical terms

Ocean acidification: The process by which increased atmospheric CO₂ dissolves in seawater, lowering pH and carbonate ion concentration.

Biomineralisation: Biological process by which marine organisms precipitate minerals to form hard structures, such as echinoderm skeletons.

High-magnesium calcite: A form of calcite containing elevated magnesium levels, common in echinoderm skeletons and highly soluble under acidified conditions.

Aragonite saturation state: A measure of the thermodynamic potential for aragonite (a calcium carbonate polymorph) to precipitate or dissolve in seawater; lower values indicate greater risk of dissolution.

Mg/Ca ratio: The molar ratio of magnesium to calcium in seawater, which influences the mineralogy and mechanical properties of echinoderm skeletons.

pCO₂: Partial pressure of carbon dioxide in seawater, reflecting CO₂ levels and used to simulate future acidification scenarios in experiments.

References

1. Calcium-rich seawater affects the mechanical properties of echinoderm skeleton. Communications Earth & Environment (2024).
2. Skeletal Mg content in common echinoderm species from Deception and Livingston Islands (South Shetland Islands, Antarctica) in the context of global change. Marine Pollution Bulletin (2023).
3. Calcite-aragonite seas as a driver of echinoderm evolution? Experimental insight and deep-time decoupling. Geology (2023).
4. Interactive effects of near-future temperature increase and ocean acidification on physiology and gonad development in adult Pacific sea urchin, Echinometra sp. A. Coral Reefs (2014).
5. Cascading Effects of Ocean Acidification in a Rocky Subtidal Community. PLOS ONE (2013).